Underfloor heating problem

I had a guy do some work on my house including installing wet underfloor heating before the screed in my extension went down. I have a hetta system with two zones. I zone for the conservatory and 1 zone (with 2 pipe runs) for the lounge. The guy who did it did some other work for me and he turned out to be a bit of an idiot. Basically didn’t actually get anything right so I wasn’t surprised when the underfloor heating didn’t work. I am trying to debug it as was getting no flow at all initially. Firstly he had installed the flow and return to the pump the wrong way around. Changed that to the correct way and now I do get some flow under certain conditions. He must have mixed up the pipes as when I put on zone 1 the first two actuators open And I get flow on the first and 3rd flow meters. But I only get flow if I either turn the blending valve up high so that the temp on the value is higher than the actual water coming in or I turn the target temperature of the boiler right down. As soon as the temp of the water coming out from the boiler exceeds the 45 on the blending value dial it shuts down the flow and basically just sits there. It doesn’t seem to ever cool down enough to start up again. It would be great if anybody has any ideas or could see if the layout looks right. Thanks very much in advance

Just in case anybody else has this problem I think I’ve worked out it’s a blocked pump. The blending valve is shutting flow to the circuit and because the Grundfos pump is blocked it’s not circulating water through the UFH pipes and hence the temp isn’t dropping down as it should so the blending valve doesn’t ever reopen.